1. Field of the Invention
The present invention relates to a structure of an ink-jet printing device containing an ink-jet printing head for discharging ink droplets from a nozzle.
2. Discussion of Related Art
An ink-jet printing device prints an image on a sheet placed on a platen by discharging ink droplets from an ink-jet printing head. The ink-jet printing head includes a plurality of nozzles. Generally, the nozzles discharge black ink and color inks, such as yellow ink, magenta ink, and cyan ink. In this case, each nozzle does not discharge all the color inks, and nozzles corresponding to the respective inks are determined in advance.
The ink-jet printing device is not necessarily used constantly. When it is used as a family device, it is supposed that the frequency of usage is low. When the ink-jet device is not used, it is exposed to the outside air. When the nozzles of the ink-jet printing head are exposed to the outside air, ink in the nozzles becomes dried, and viscosity of the ink increases. Even when printing is performed frequently, an image formed on the sheet is not necessarily a color image using multi-color ink. As a result, ink droplets are not discharged constantly from all the nozzles. Therefore, in the nozzles which are used less frequently, ink becomes dried in the nozzles, increasing the viscosity of the ink. Assuming that the ink is dried in the nozzles, and the viscosity of the ink is increased, the ink droplets cannot be discharged desirably from the nozzles. Therefore, in the related art, the ink-jet printing device is provided with a waiting cap member for sealing the nozzles of the ink-jet printing head when not actively printing. In addition, in order to solve or prevent clogging of the nozzles due to increase in viscosity of ink, a purging device for sucking ink from the nozzles is also provided. The purging device includes a purging cap member for covering the ink-jet printing head, so as to enclose the nozzles, and a sucking unit connected to the purging cap member. When the sucking unit is activated, the pressure in the purging cap member is lowered, whereby ink is sucked from the nozzles. By sucking the ink from the nozzles, increases in the viscosity of the ink in the respective nozzles are avoided. In this manner, clogging of the nozzles is solved. The waiting cap member and the purging cap member may be composed separately or may be identical, depending on the type of the ink-jet printing device.
In order that the sucking unit sucks the ink desirably, it is necessary that the purging cap member encloses the nozzles hermetically without fault. In order to do so, it is preferable that the purging cap member is formed of a material having sufficient flexibility. However, in order to achieve reliable suction of ink from the nozzles, it is necessary to lower the pressure in the cap member significantly. Therefore, the purging cap member is required to have sufficient rigidity, such that deformation of the purging cap is prevented even when the pressure in the interior of the purging cap is less than the pressure outside the purging cap. This is because deformation of the purging cap member hinders the purging cap member from hermetically enclosing the nozzles. In addition, when a deformed purging cap member comes into contact with the nozzles, ink meniscuses formed in the respective nozzles are broken, and suction of ink from the respective nozzles may be impaired.
In the ink-jet printing device in the related art, various improvements are made to the cap member for achieving both flexibility for enclosing the nozzles hermetically, and rigidity for preventing the cap member from being easily deformed during ink suction. For examples of such improvements, see JP-A-2005-161803, JP-A-2003-1839, JP-A-2000-238276, and JP-A-2000-52567.
In recent years, the ink-jet printing head has been upsized in order to print the image more precisely at a high speed. In addition, the number of nozzles has been increased. As a result, the cap member has been upsized, requiring the sucking unit to provide a greater suction force. When the suction force provided by the sucking unit is increased, the likelihood of cap member deformation is increased, and a new countermeasure for preventing such deformation is required.